كتاب متميّز
Introduction
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3.6. Kidneys 3.6.1.Gross (macroscopic) anatomy Lying in a retroperitoneal position, the bean-shaped kidneys can be measured reliably in maximum longitudinal axis (about 11cm in the middle-aged adult), the left kidney lies in a more cranial position (and is thus more covered by the lower ribs). The vascular anatomy of the kidney hilum with its branched vessels (ventral vein and dorsal artery) and the urinary tract (pelvis), and the origin of the ureters are important aspects for ultrasound examinations. As are the other two layers of the parenchyma, the cortex and the medulla containing the 9-11 papillae leading to the calices and the pelvis. The kidneys lie on the psoas muscles, adjacent to the right liver lobe or the spleen respectively, and to intestinal structures which cover the organs ventrally The normal adrenal glands are too small for routine detection by ultrasound examination.
3.6.2.Examination technique and ultrasound (sectional) anatomy The kidneys should be examined routinely in both the left and right oblique position, scanning the right and the left kidney in all planes longitudinal to the organ`s main axis. Sections should then be taken transverse to this axis to complete the examination and reveal a typical horseshoe-shape to the kidney hilum. The vasa arcuata separate the cortex from the medulla. The papillae are typically cylindrical and are echopoor due to their high fluid content Respiratory manoeuvers can be helpful by observing the gliding movement of the kidney on the psoas muscle. In cases of right sided pain, palpation of the kidneys under ultrasound control is helpful to localize the site of pain more precisely. Reduction in parenchymal width is a normal part of the ageing process.
3.6.3. Pathology One of the advantages offered by routine ultrasound is the possibility of detecting asymptomatic kidney tumors. Their detection at a curative stage is possible and therefore careful study of the kidney is mandatory for any abdominal ultrasound examination. Kidney cysts and occasionally haemangioleiomyomas are also easily detectable focal lesions.Aside from focal lesions the other main pathology detectable on ultrasound is that of urinary tract obstruction. The normal pelvis which is usually a flat and liquid-poor structure that is hardly visible, becomes more or less balloon-shaped and as with biliary obstruction, the site and the cause of the obstruction to flow can often be detected on ultrasound particularly when taken in combination with clinical history, physical examinations and laboratory findings.
3.7. Spleen The spleen is enveloped by the left diaphragm and its lower pole reaches the upper pole of the kidney. The hilum is marked by the branching splenic vein and the tail of the pancreas. Measurement of the size is unprecise in the longitudinal axis but as a routine, the transverse diameter should not exceed 6 cm in the middle-aged or older adult. Larger diameters are considered to be normal in young individuals and especially in children. Inflammatory or congestive enlargement of the spleen is usually easily explained by other pathology (e.g. liver cirrhosis). Focal lesions in the (usually enlarged) spleen are predominantly malignant such as with splenic involvement in systemic disease (e.g. lymphoma). Benign focal splenic lesions (cysts, abscesses, hemangioma etc.) are rare as is metastatic disease to the spleen from solid malignancies.
3.8. Pelvis The urinary bladder, the internal genitalia (prostate and seminal vesicles, uterus, ovaries and vagina) and the great vessels (internal and external iliac arteries) are the pelvic organs most easily accessible to ultrasound examination, especially using a fluid filled urinary bladder to create a good acoustic window which can help to push away loops of intestine. Ultrasound examination of the pelvis is concerned with cystic and solid masses, urinary obstruction of the bladder (residual urine volume) or the ureter and processes involving thickening of the wall.
The intestinal tube has an anatomically uniform layer structure which is best visible in the stomach by transcutaneous ultrasound. Here the muscle layer is especially thick. A clearly layered structure, however, can be just as well seen in the subdiaphragmatic portion of the esophagus and in the rectum. Small intestinal loops are detectable in normal conditions as an intermittently, slightly fluid filled region with active peristalsis. Colonic sections normally demonstrate a typical shape - due to the haustrae, a strongly reflective gas content, and no peristalsis. An enhanced fluid content of the gastric/intestinal lumen, its wall structures and/or the surrounding abdominal cavity will result in improved ultrasound visualisation of the sections concerned. This is true in intestinal obstruction (ileus, subacute-ileus), inflammatory wall thickening, and in ascitic, bloody, lymphatic or mixed fluid collections in the peritoneal cavity.
Minor amounts of pathological fluid collections in the abdomen can easily be detected in the pouch of Douglas. Focal lesions of the intestinal wall such as inflammatory or malignant lesions are difficult to differentiate from the surrounding tissues (omental structures) unless they lead to intestinal obstruction, to parenchymal infiltration (e.g., into the liver), or to abscess or ascites formation. The same is true with metastatic involvement of the peritoneum. Transcutaneous abdominal ultrasound in diseases of the intestine and the peritoneal cavity is a fascinating area which is still under-evaluated (as opposed to endoscopic ultrasound whose value might well be over-estimated).
During routine ultrasound examination attention should be given to the possibility of pathology occuring in non-abdominal regions and organs. In the pleural cavitiy which is not usually visible, ultrasound can show even smaller amounts of fluid which may not be seen on plain X-ray films of the thorax. Diagnostic puncture of this fluid under ultrasound guidance is an easy and safe subsequent diagnostic procedure particularly if malignancy is suspected. In the case of larger effusions, pleural drainage under ultrasound guidance is the method of choice. The same is true of parenchymal lung lesions provided they are not covered by air containing surrounding lung tissue. Diagnostic and therapeutic puncture procedures are preferably guided by ultrasound (and not by CT). Pericardial effusions likewise should not be under-estimated, their ultrasound detection leading to appropriate cardiological assessment and therapy. The possibility of diagnostic ultrasound for other soft tissue diseases such as abscesses, lymphomatous infiltration and other pathological masses or fluid collections are worth mentioning. They deserve, however, specialized consideration as does the application of ultrasound in bone and joint disease.
4. General considerations Clearly ultrasonography has advantages and of course some limitations. The advantages are: - easy and immediate availability - safety - lack of radiation - reproducability and repeatability - low hardware and manpower cost - speed - high information per case - complimentary to other modalities eg endoscopy. For the individual clinician to perform his own abdominal ultrasound also has the advantage of improved patient care and the personal, professional satisfaction that comes with this. In Germany, clinical ultrasonography is an indispensable tool for any doctor treating abdominal disease, so any young medical colleague will be given an intensive individual training in ultrasonography in any species making use of diagnostic and interventional ultrasonography (internal medicine, cardiology, surgery, ENT, gynecology and obstetrics, dermatology, intensive care unit, and so on). The disadvantages of abdominal ultrasound are: - examiner dependent (which is, however, the case in CT-, MRI-scanning as well) - limited spread and under-evaluation by clinicians - deficiencies in routine docu-mentation due to different zooms, positioning of the probe, different reflexibility of the same organs in different patients,anatomical variations, etc) - limited views in regions cov- ered by gas or bone - limited information in bowel diseases (which is no problem for the GI-tube orientated endoscopist). To perform clinical ultrasound effectively involves a constant process of looking, searching the normal anatomy including possible variations and combining data from the patient’s history and physical examination with the realtime section of information available on the screen. This may subsequently need to be further incorporated with the information available from laboratory data. The continuing process of interpreting two dimensional sections into three dimensional organs and regions must go on in the examiners mind and these processes require an amount of clinical experience. CT scanning is often regarded as the most effective imaging modality for abdominal work but in most cases it would only confirm findings discovered by an effective abdominal ultrasound without providing further information. A focal lesion on ultrasound remains - as a rule - a focal region on CT. An exception to this is the retroperitoneal region and the pelvis where better anatomical views will be more easily provided by CT scanning. But, as for any diagnostic procedure, CT scanning quality may differ considerably dependent on the examiner (as well as in any imaging modality), the generation of scanner used and the time spent on the procedure. As a general rule, ultrasound is superior to CT in slim individuals whereas CT resolution is improved by broad, fatty layers. The local resolution capacity in parenchymal organs is superb in ultrasound, much better as compared to CT- or MRI-scanning. Ultrasound is not bound by fixed sections like CT scanning, which is a great advantage in a given anatomy to achieve optimized sectional information. Some problems beginners have may be related to the high inter-individual variability particularly related to normal anatomy etc. Nevertheless, virtually everybody has – for example - a liver, a gallbladder and a kidney in the right upper abdomen and it is no problem to see these organs. Once they are discovered and the great vessels are seen, systematic ultrasound examination and evaluation of the abdomen is no longer a problem. It may start as a time consuming activity, about 15-20 minutes per case in the first 100 patients or so, but this investment will be re-imbursed to a great extent. The necessity to look at all organs in an abdominal ultrasound provides a good training summating the experience and data necessary to become familiar within normal pathological and doubtful findings. The latter category becomes less with every patient examined but will never reach zero which should stimulate not only the attention of the beginner but also in the most experienced ultrasonographer (making ultrasound examination a never ending challenge similar to physical examination and similar to asking for the patient`s history). As far as measuring of biological structures is concerned, some limitations are obvious. The morphological appearance is usually a more important element than measurement. For example in the common bile duct, 11mm diameter in the prepancreatic portion with a slim duct towards the liver hilum would be normal whereas a diameter of 7mm in all sections including the intrahepatic bile ducts is highly suggestive of an increased ductular pressure. When measuring parenchymal organs you must always keep in mind that variations of the normal are numerous and a simple truth is that large individuals will have bigger internal organs compared to small people and that young individuals tend to have more parenchymal volume (e.g. in the kidneys) as compared to elder individuals. The question of background phenomena is easy but important. A bright spot is better seen against a not so bright background and therefore before a dark surface which is even more important in areas of limited or weak brightness. Since the ultrasound picture is brightness modulated (realtime B picture), and since in a given organ the brightness can vary considerably from individual to individual, a light spot of identical brightness might be visible in one person’s liver and hardly detectable in another. Therefore the size from which eg a liver metastasis can be visualised reliably on ultrasound cannot be given as a constant figure. In a bright fatty liver the (usually) less echogenic metastasis can be seen at diameters even under 10mm where in a dark liver with a high fluid content like in right heart failure even a large echo-poor lesion will hardly be detectable. Finally, especially important is the fact that the beginner must recognise that a finding and a diagnosis are often not the same – a problem not at all exclusively related to ultrasound. And as with any new procedure, the learning curve is individually differering from physician to physician.
Clinical
ultrasonography is beautiful – and helpful for all our patients.
Lucas Greiner, MD ® lgreiner@wuppertal.helios-kliniken.de
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